← Microsoft Interview Insights

Microsoft·Product Manager·Onsite - Product Sense / Strategy·Intermediate

Intermediate
May 2026

Summary

PM interview at Microsoft, just one question about estimating Slack's daily message volume. Short and focused, felt more like a warmup than a full round.

Questions Asked (1)

Q1

Estimate how many Slack messages are sent globally per day.

Product Analytics & MetricsProduct Sense & Ideation
Author's notes

Classic estimation question.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Break the problem into a top-down estimation: start with the total number of Slack users, then estimate the percentage who are daily active, and finally estimate the average number of messages sent per active user per day. Use round numbers and state assumptions clearly to keep the calculation simple and defensible.

Pro tip: Show that you understand the difference between consumer and enterprise usage patterns—most Slack messages come from paid workspaces, so focus on that segment and mention that direct messages and channel messages have different volumes.

1. Define the scope and key variables

Clarify that you're estimating global Slack messages per day, including all message types (channels, DMs, group DMs) from both free and paid workspaces. Identify the key variables: total users, daily active users (DAU), and messages per DAU.

2. Estimate total Slack users

Start with a known figure: Slack has over 20 million daily active users (as of 2023). If unsure, estimate from Microsoft Teams' user base or overall knowledge worker population. Assume ~20M DAU globally.

3. Estimate messages per active user per day

Consider that an average active user might send 10-20 messages per day, but this varies by role. Use a midpoint like 15 messages per day. Adjust for power users vs. light users if needed.

4. Calculate and sanity-check

Multiply 20M DAU by 15 messages/day to get 300M messages per day. Sanity-check against known benchmarks (e.g., Slack reported 1B+ messages per week in 2019, which is ~150M/day; adjust for growth).

5. Present the final estimate with assumptions

State the final estimate (e.g., 300-500M messages per day) and summarize key assumptions. Offer to refine if given more data.

Key Points to Mention

  • Distinguish between daily active users (DAU) and total registered users.
  • Consider that most messages come from paid workspaces, which have higher engagement.
  • Account for different message types: channels, DMs, and threads.
  • Use round numbers and simple math to avoid calculation errors.
  • Sanity-check your estimate against publicly known Slack metrics (e.g., 1B messages per week in 2019).
  • Acknowledge that the estimate is a range, not a precise number, and state assumptions clearly.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.